Membrane bonding

ABSTRACT

Systems and techniques are provided for membrane bonding. A bonding agent may be applied to one or both of an ultrasonic device and membrane. The membrane may be placed on the ultrasonic device such that the membrane is in contact with the ultrasonic device through the bonding agent. The membrane and the ultrasonic device may be placed in between a first flat plate and a second flat plate, such that the second flat plate rests on top of the membrane. Light pressure may be applied to the membrane. The light pressure may be applied by one or more of the weight of the second flat plate and a pressure providing device applying pressure to either or both of the first flat plate and the second flat plate.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims priority to U.S. Provisional Patent Application No. 62/164,108, filed on May 20, 2015.

BACKGROUND

Electromechanically active devices may be used in a variety of applications. For example, electromechanically active devices may be used in transducers, sensors, and, actuators. In some uses, the electromechanically active device may be used to generate soundwaves, including ultrasonic sound waves, through vibration of the electromechanically active device. A membrane, or diaphragm, may be added to the electromechanically active device to provide additional surface area to move a medium, such as the air, with the vibrations of the electromechanically active device. The membrane may be tuned to optimize various parameters of the performance of the electromechanically active device, such as enabling efficient energy transfer between different media or tuning resonant performance of the electromechanically active device to a specific frequency.

BRIEF SUMMARY

According to an implementation of the disclosed subject matter, a bonding agent may be applied to one or both of an ultrasonic device and membrane. The membrane may be placed on the ultrasonic device such that the membrane is in contact with the ultrasonic device through the bonding agent. The membrane and the ultrasonic device may be placed in between a first flat plate and a second flat plate, such that the second flat plate rests on top of the membrane. Light pressure may be applied to the membrane. The light pressure may be applied by one or more of the weight of the second flat plate and a pressure providing device applying pressure to either or both of the first flat plate and the second flat plate.

A stencil may be placed on an ultrasonic device such that the stencil covers one or more ultrasonic transducers of the ultrasonic device. The stencil may include one or more openings. An epoxy may be applied to the ultrasonic device through the one or more openings of the stencil. The epoxy may form epoxy lines on the ultrasonic device. The epoxy may be applied to electromechanically active devices of the ultrasonic transducers. The stencil may be removed from the ultrasonic device. A membrane may be placed on the ultrasonic device such that the membrane is in contact with the epoxy. The membrane may cover one or more of the ultrasonic transducers. The membrane and the ultrasonic device may be placed between a first flat plate and a second flat plate, such that the second flat plate is in contact with the membrane and the first flat plate is in contact with the ultrasonic device opposite the second flat plate. Light pressure may be applied to the membrane or the ultrasonic device through either or both of the first flat plate and the second flat plate for at least part of the curing time of the epoxy.

Systems and techniques disclosed herein may allow for membrane bonding. Additional features, advantages, and embodiments of the disclosed subject matter may be set forth or apparent from consideration of the following detailed description, drawings, and claims. Moreover, it is to be understood that both the foregoing summary and the following detailed description are examples and are intended to provide further explanation without limiting the scope of the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included to provide a further understanding of the disclosed subject matter, are incorporated in and constitute a part of this specification. The drawings also illustrate embodiments of the disclosed subject matter and together with the detailed description serve to explain the principles of embodiments of the disclosed subject matter. No attempt is made to show structural details in more detail than may be necessary for a fundamental understanding of the disclosed subject matter and various ways in which it may be practiced.

FIG. 1 shows an example ultrasonic device according to an implementation of the disclosed subject matter

FIG. 2 shows an example stencil according to an implementation of the disclosed subject matter.

FIG. 3 shows an example ultrasonic device according to an implementation of the disclosed subject matter.

FIG. 4 shows an example of an ultrasonic device according to an implementation of the disclosed subject matter.

FIG. 5 shows an example of membrane bonding according to an implementation of the disclosed subject matter.

FIG. 6 shows an example ultrasonic transducer cell according to an implementation of the disclosed subject matter.

FIG. 7 shows an example ultrasonic transducer cell according to an implementation of the disclosed subject matter.

FIG. 8 shows an example ultrasonic transducer cell according to an implementation of the disclosed subject matter.

FIG. 9A shows an example ultrasonic device according to an implementation of the disclosed subject matter.

FIG. 9B shows an example ultrasonic device according to an implementation of the disclosed subject matter.

FIG. 10 shows a process suitable for membrane bonding according to an implementation of the disclosed subject matter.

DETAILED DESCRIPTION

According to embodiments disclosed herein, membrane bonding may allow for the bonding of a membrane to an electromechanically active device.

An ultrasonic device may include ultrasonic transducers on a substrate, such as on a Printed Circuit Board (PCB.) An ultrasonic transducer may include an electromechanically active device, such as a cantilever or flexure, attached to the wall of a cavity in the substrate. A stencil may be placed over the ultrasonic device. The stencil may be used to apply epoxy in a border around individual ultrasonic transducers and to the tips of the electromechanically active devices. A membrane may be placed on top of the ultrasonic device and pressed into the epoxy. The ultrasonic device, with the membrane, may be placed between flat plates, which may be used to apply light pressure to the ultrasonic device and membrane. The ultrasonic device and membrane may be left under pressure for the cure cycle of the epoxy. After the epoxy has cured, the membrane may be bonded to the ultrasonic device, with each ultrasonic transducer of the ultrasonic device being bonded to a separate section of the membrane. Bond lines of epoxy may separate the sections of the membrane, allowing them to move separately.

An ultrasonic device may include transducers on a substrate. The substrate may be any suitable material, and may be, for example, a PCB with any suitable number of layers. The substrate may be in any suitable shape, and the surface of the substrate may be flat, or may be curved or textured in any suitable manner. A transducer of an ultrasonic device may include an electromechanically active device attached to a wall of a cavity in the substrate. The electromechanically active device may be a cantilever or flexure, and may be, for example, a piezoceramic unimorph or bimorph. The cavity may be any suitable shape and depth. For example, the cavity may be circular. The cavity may be created in the substrate in any suitable manner, including through subtractive processes, such as drilling, or additive processes. The electromechanically active device may be attached to the wall of the cavity in any suitable manner. For example, a step structure may be created on an edge of the cavity, and the electromechanically active device may be bonded to the step structure using any suitable adhesive, such as, for example, conductive epoxy. The electromechanically active device may be any suitable length and width for vibration at ultrasonic frequencies, and may be oriented in the cavity at any suitable angle. For example, the electromechanically active device may reach approximately halfway across the cavity. The top surface of the electromechanically active device, which may be, for example, a passive material of a unimorph or an active material of a bimorph, may be level, or near-level, with the top of the cavity. In some implementations, a transducer may include more than one electromechanically active device within a cavity. The ultrasonic device may include any number of ultrasonic transducers in any suitable arrangement.

A membrane may be bonded to the ultrasonic device to create an ultrasonic device with a membrane. The membrane and electromechanically active devices of an ultrasonic device may be cleaned using any suitable solvents and acids. For example, acetone, methanol, isopropanol may be used to clean bonding surfaces of the electromechanically active devices. Chromic acid, hydrochloric acid, and other suitable substances or materials which may be promote adhesion may also be used to clean the electromechanically active devices. The electromechanically active devices may also be cleaned using an ultrasonic bath or plasma etching. The membrane may be cut larger than the area needed to cover the ultrasonic device. The membrane may be any suitable material or composite material structure, which may be of any suitable stiffness and weight, for vibrating at ultrasonic frequencies. For example, the membrane may be both stiff and light. For example, the membrane may be aluminum shim stock, metal-patterned Kapton, or any other metal-pattern film. The membrane may be impedance matched with the air to allow for more efficient air-coupling of the ultrasonic transducers. The membrane may include additional structures, such as, for example, ring structures located on the membrane where the membrane will contact the tips of the electromechanically active devices. After being cut, the side of the membrane which will be bonded to the ultrasonic device, or bonding surface, may have surface preparations applied to promote adhesion of an epoxy. These preparations may include plasma cleaning, chemical etching, mechanical texturing, or chemical activation. For example, the bonding surface of the membrane may be textured using sandpaper, an abrasive cleaning pad, or an abrasive slurry. The bonding surface of the membrane may be cleaned using isopropanol.

An epoxy or other suitable bonding agent may be used to bond the membrane to the ultrasonic device. The membrane may be bonded to the substrate of the ultrasonic device, as well as to the electromechanically active devices of the ultrasonic transducers. The epoxy may be conductive or non-conductive. The epoxy may have a high viscosity while still being spreadable. The epoxy may have any suitable curing schedule. For example, the epoxy may have a curing schedule that may allow the epoxy to cure while staying below 90 degrees Celsius. This may allow the epoxy to be cured without causing an electrically active material, such as a piezoceramic, of an electromechanically active device to reach its Curie temperature during the curing of the epoxy. The epoxy may cure within 48 hours. The epoxy may be mixed with glass microspheres whose diameter falls within a given range and that may have a target size. The diameters of the spheres may be narrowly distributed about the target size. For example, if the target size is 100 micrometers, then over 95% of the spheres may have diameters within a few percent of 100 micrometers. The glass microspheres may have any suitable diameter, such as from 10 to 100 micrometers in diameter. The glass microspheres may be used to determine the thickness, up from the surface of the ultrasonic device, of the bond lines formed by the cured epoxy, as the bond may be as thick as the thickness of the glass microspheres. The glass microspheres may also allow the epoxy to form standoffs between the tips, of the electromechanically active devices and the membrane, separating them by more than just the thickness of the epoxy alone. The amount of glass microspheres mixed with the epoxy may be high enough to allow proper distribution of the glass microspheres throughout the epoxy and low enough to not alter the properties of the bond formed by the cured epoxy in any significant manner. When pressure is applied to the bond, the glass microspheres of a given diameter may stop the two sides from moving together so that the separation between the sides is about equal to the given diameter of the microspheres.

The epoxy may be applied to the ultrasonic device. For example, the epoxy may be applied using screen printing techniques. A stencil may be placed over the ultrasonic device. The stencil may be made of any suitable material, including metal, such as stainless steel, or polyimide, may be of any suitable thickness, for example, from 25 micrometers to 100 micrometers thick, and may be patterned. For example, the stencil may be stainless steel that is 50 micrometers thick. The pattern of the stencil may include openings or apertures, which may be in any suitable shapes, such as, for example, squares, circles, and hexagons. The pattern of the stencil may, for example, include an array of dashed squares with dots at the center. The dashed squares may be patterned with any suitable number of dashes. For example, each dashed square may have two dashes per side, with sides shared by neighboring squares. The size of the dashed squares may define the size of an ultrasonic transducer cell of the ultrasonic device. The width of the dashes may affect the size of the ultrasonic transducers cells, and the area of the section of the membrane that moves, and may be as thin as possible in order to allow for larger ultrasonic transducer cells. In some implementations, the stencil pattern may result in an ultrasonic transducer cell including more than one ultrasonic transducer. The dots may be positioned such that epoxy applied through the dots when the stencil is placed over the ultrasonic device may be deposited onto the tips of the free ends of the electromechanically active devices. The stencil may be placed over the ultrasonic device using predrilled fiducials in both the stencil and the ultrasonic device to obtain proper alignment. Epoxy may be spread over the stencil using a metal straight edge or non-compliant rubber squeegee, applying the epoxy to the ultrasonic device through the openings in the stencil. For example, the epoxy may form squares, or dashed squares, around each ultrasonic transducer, with a dot of epoxy applied to the tip of the free end of each ultrasonic transducer's electromechanically active device. The stencil may be removed after the epoxy has been applied.

The ultrasonic device, with applied epoxy, may be placed on a first flat plate, which may rest on or be attached to a surface. The first flat plate may be any suitable material, and any suitable thickness. The membrane may be placed onto the ultrasonic device. The membrane may be placed with the prepared bonding surface of the membrane coming into contact with the epoxy on the ultrasonic device. A second flat plate may be placed on top of the membrane, and may be used to apply light pressure to the membrane and ultrasonic device, ensuring contact between the membrane and the epoxy on the ultrasonic device. The light pressure may be, for example, ¼ PSI or above while being below a pressure level that would crack the glass microspheres of the epoxy Pressure may be applied in any suitable manner, including, for example, through the weight of the second flat plate on top of the membrane, or through a pneumatic cylinder or other pressure providing device which may be used to provide a controlled amount of sustained pressure to the second flat plate. The light pressure may be kept on the membrane for the duration of the cure cycle of the epoxy, or may be removed part way through the cure cycle. In some implementations, pressure may be provided by the weight of the first flat plate. For example, the membrane may be placed on top of the second flat plate, with the ultrasonic device on top of the membrane. The first flat plate may then be placed on top of the ultrasonic device, with the weight of the first flat plate applying pressure that may push the ultrasonic device towards the membrane. The first flat plate may also be attached to a pressure providing device instead of, or along with, the second flat plate.

When the cure cycle of the epoxy has completed, the ultrasonic device with attached membrane may be removed from between the flat plates. The membrane may be attached to the ultrasonic device along bond lines formed by the cured epoxy. The bond lines may reflect the pattern of the stencil, for example, forming a grid and dividing the ultrasonic device into square ultrasonic transducer cells. The membrane may also be bonded to the tips of the free end of each electromechanically active device of the ultrasonic device. This may result in each ultrasonic transducer being covered with a section of the membrane that is bonded to the substrate of the ultrasonic device around the ultrasonic transducer and also bonded to the tip of the free end of the ultrasonic transducer's electromechanically active device. The tip of the free end of the electromechanically active device may be slightly off being aligned with the center of the section of the membrane. This may allow the section of the membrane to be pushed outward by the electromechanically active device so that the highest point of the section of the membrane is at the center of the section of the membrane. Each section of the membrane may be able to move independently of any other section of the membrane, though the membrane may remain a single piece of material. The bond lines formed by the cured epoxy may mechanically isolate the sections of the membrane from each other. The movement of one section of the membrane may not be transmitted across a bond line, where the membrane is bonded to the substrate, to another section of the membrane.

In some implementations, the epoxy or other suitable bonding agent may be applied directly to the bonding surface of the membrane in addition to, or in lieu of, of the application of the epoxy or bonding agent to the ultrasonic device. The epoxy or bonding agent may be applied to the bonding surface of the membrane using screen printing techniques and a stencil. The stencil may include the same pattern as the stencil that may be used to apply epoxy or a bonding agent to the ultrasonic device, or may have a different, for example, complementary, pattern. For example, a stencil may be used to apply epoxy to the bonding surface of the membrane to form a grid pattern, while a second stencil may be used to apply epoxy dots to the tips of the free ends of the electromechanically active devices.

In some implementations, more than one membrane may bonded to an ultrasonic device. For example, multiple separate membranes of the same material, or different materials may be used to cover the ultrasonic transducers of an ultrasonic device. Different materials may be used, for example, to allow different sections of the ultrasonic device to have different operating characteristics.

FIG. 1 shows an example ultrasonic device according to an implementation of the disclosed subject matter. An ultrasonic device 100 may include a substrate 160 and ultrasonic transducers 110. The ultrasonic transducers 110 may include a main cavity 130, a secondary cavity 140, a channel 150, and an electromechanically active device 120. The substrate 160 may be any suitable substrate, such as, for example, a PCB, and may be in any suitable shape and of any suitable thickness. The substrate 160 may include any number of fiducials, which may be, for example, predrilled. The first cavity 130 may be a cavity in the substrate 160, formed through any suitable additive or subtractive processes, and may be any suitable shape and any suitable depth. For example, the cavity 160 may be circular. The second cavity 140 may be a cavity in the substrate 160 which may overlap the first cavity 130, and may any suitable shape and any suitable depth. For example, the second cavity 140 may be a circular cavity of less depth than the first cavity 130, forming a first stair step at its intersection with the first cavity 130. The channel 150 may be a channel of any suitable width and depth, made in any suitable manner, which may run through the centers of the first cavity 130 and the second cavity 140. For example, the channel 150 may be made using a dicing saw cut of any suitable width through the first cavity 130 and the second cavity 140. The channel 150 may be shallower than the second cavity 150, so that the channel forms second stair step where it overlaps the second cavity 150. The second stair step may be in alignment with the first stair step. The channel 150 may run across a number of ultrasonic transducers 110, for example, if the ultrasonic transducers 110 are aligned on the substrate 660 so that a straight line cut from a dicing saw may pass through the centers of all of the first cavities 130 and second cavities 140 in a group of aligned ultrasonic transducers 110.

The electromechanically active device 120 may be any suitable electromechanically active device such as, for example, piezoelectric unimorph or bimorph which may use piezoceramic material bonded to an electrically inactive substrate. The electromechanically active device 120 may be any suitable shape, and may, be for example, a cantilever or flexure. The electromechanically active device 120 of the ultrasonic transducer 110 may be bonded to the substrate 160 at the first and second stair steps, with the free end of the electromechanically active device 120 projecting out over the bottom of the first cavity 130. The first and second stair steps may also include electrodes connected to vias which may go into the substrate 160, and may be bonded to electrodes of the electromechanically active device 120 using conductive epoxy. The top surface of the electromechanically active device 120 may be level with, or slightly below, the top surface of the substrate 160.

FIG. 2 shows an example stencil according to an implementation of the disclosed subject matter. A stencil 200 may include any suitable pattern of openings in any suitable shapes. The shapes may be, for example, squares, circles, rectangles, hexagons, octagons, other regular irregular polygons, or irregular shapes, and may be arranged in any suitable pattern, including a square grid, hex grid, concentric circles or other regular or irregular pattern. The stencil 200 may include any combination of shapes in any combination of patterns. For example, the stencil 200 may include a dashed squared pattern including dashed squares 210. The dashes 220 may be openings in the stencil, and may form a pattern of dashed squares 210 with shared sides. Any number of dashes 220 may be used to form each side of the dashed squares 210 of the stencil 200. The center of each of the dashed squares 210 may include a dot 230, which may be a circular opening in the stencil 200, or may be any other suitably shaped opening. The stencil 200 may have any suitable thickness, and may be, for example, between 25 micrometers and 100 micrometers thick. The stencil 200 may be made from any suitable material, including metals and polyimides. For example, the stencil 200 may be 50 micrometer thick stainless steel. The stencil 200 may include any suitable number of fiducials, which may be, for example, predrilled, to allow for alignment of the stencil 200 with the ultrasonic device 100 based on the fiducials of the substrate 160.

FIG. 3 shows an example ultrasonic device according to an implementation of the disclosed subject matter. The electromechanically active devices 120 of the ultrasonic device 100 may be cleaned using solvents and acids. For example, acetone, methanol, and isopropanol may be used to clean the electromechanically active devices 120. Chromic acid, hydrochloric acid, and various other materials which may promote adhesion may also be used.

The stencil 200 may be placed over the ultrasonic device 100. The stencil 200 may be aligned with the ultrasonic device 100 so that the dots 230 are placed over the tips of the free ends of the electromechanically active devices 120. Fiducials on the stencil 200 and the substrate 160 may be used to obtain proper alignment of the stencil 200 with the ultrasonic device 100. Epoxy may be applied to the ultrasonic device 100 through the stencil 200 using screen printing techniques. For example, epoxy may be applied through the openings in the stencil 200, such as the dashes 200 and the dots 230, by using a metal straight-edge or non-compliant rubber squeegee to spread epoxy over the stencil 200. The epoxy may be any suitable epoxy or other bonding agent, may be conductive or non-conductive, and may have a high viscosity while still being spreadable. The epoxy may having a curing schedule that allows the epoxy to cure at temperatures below 90 degrees Celsius, and to cure within 48 hours. The epoxy may be mixed with glass microspheres, which may between 10 micrometers and 100 micrometers in diameter. Enough glass microspheres may be used to allow the glass microspheres to be distributed throughout the epoxy without significantly impacting the properties of the bond formed by the curing the epoxy.

After the epoxy is applied to the ultrasonic device 100, the stencil 200 may be removed. The epoxy applied to the ultrasonic device 100 through the stencil 200 may form epoxy lines 320 and epoxy dots 330. The epoxy lines 320 may form a pattern on the ultrasonic device 100 similar to the pattern of the stencil 200, for example, forming ultrasonic transducer cells 310 which may be the same size as the dashed squares 210 of the stencil 200. The epoxy dots 330 may be located on the tips of the free ends of the electromechanically active devices 120.

In some implementations, the pattern of the stencil 200 may result in different numbers of ultrasonic transducers 110 being included within a single ultrasonic transducer cell 310. For example, each ultrasonic transducer cell 310 may include only one ultrasonic transducer 110, or may include two or more ultrasonic transducers 110.

FIG. 4 shows an example of an ultrasonic device according to an implementation of the disclosed subject matter. A membrane 400 may be cut to an appropriate size for the ultrasonic device 100, for example, slightly larger than the area which the membrane 400 is intended to cover on the ultrasonic device 100. The membrane 400 may be any suitable light and stiff material for vibrating at ultrasonic frequencies, such as, for example, aluminum shim stock, metal-patterned Kapton, or any other metal-patterned film. The membrane 400 may also include suitable patterned structures. One surface of the membrane 400 may be the bonding surface, and may be prepared for bonding using plasma cleaning, chemical etching, mechanical texturing, or chemical activation. The bonding surface of the membrane 400 may also be textured using sandpaper, an abrasive cleaning pad, or an abrasive slurry. The membrane may then be cleaned, for example, with isopropanol.

The membrane 400 may be placed on the ultrasonic device 100 so that the prepared bonding surface of the membrane 400 contacts the epoxy on the ultrasonic device 100. The membrane 400 may be aligned with the ultrasonic device 100 so that it covers all of the epoxy, with the epoxy near the edges of the ultrasonic device 100 covered by the edges of the membrane 400. As the epoxy cures, the membrane 400 may be separated into membrane sections 410 along bond lines 420, which may be the result of cured epoxy lines 320.

FIG. 5 shows an example of membrane bonding according to an implementation of the disclosed subject matter. The ultrasonic device 100 with the membrane 400 may be placed in between two flat plates 510 and 520. The flat plates 510 and 520 may be made of any suitable material, and may be of any suitable thickness. Light pressure may be applied to the membrane 400 through the flat plate 510 to ensure the membrane 400 remains in contact with the epoxy on the ultrasonic device 100. The pressure may be applied through the weight of the flat plate 510, or through some pressure providing device attached to the flat plate 510 or flat plate 520. Light pressure may be kept on the membrane 400 for the entire curing cycle of the epoxy, or may be removed during the curing cycle. Once the curing cycle of the epoxy has completed, the membrane 400 may be bonded to the ultrasonic device along bond lines 420 and at the locations of the epoxy dots 330, where the electromechanically active devices 120 may be bonded to the membrane 400. This may form membrane sections 410. The membrane sections 410 may be mechanically isolated from each other by the bond lines 420, and may be able to move independently even while the membrane 400 remains in one piece. For example, when each membrane section 410 covers a single ultrasonic transducer 110, a membrane section 410 may be moved by the electromechanically active device 120 of the ultrasonic transducer 110 covered by the membrane section 410 without moving or disturbing any other membrane section 410.

FIG. 6 shows an example ultrasonic transducer cell according to an implementation of the disclosed subject matter. The ultrasonic transducer cell 310 may include the ultrasonic transducer 110, including the substrate 160, the first cavity 130, the second cavity 140, the channel 150, the electromechanically active device 120, and the membrane section 410.

FIG. 7 shows an example ultrasonic transducer cell according to an implementation of the disclosed subject matter. When the stencil 200 is used to apply epoxy to the ultrasonic device 100, the bond lines 320 may be deposited around the ultrasonic transducer 110, creating the borders of the ultrasonic transducer cell 310. The epoxy dot 330 may be located on the tip of the free end of the electromechanically active device 120, which may project out over the first cavity 130.

FIG. 8 shows an example ultrasonic transducer cell according to an implementation of the disclosed subject matter. After the membrane 400 is placed on the ultrasonic device 100 and the epoxy is cured, the membrane section 410 may be bonded along bond lines 420 to the cured epoxy around the borders of the ultrasonic transducer cell 310. The membrane section 410 may cover the ultrasonic transducer 110, and may be bonded to the electromechanically active device 120 by the epoxy dot 330.

FIG. 9A shows an example ultrasonic device according to an implementation of the disclosed subject matter. Each membrane section 410 of the membrane 400 may cover an ultrasonic transducer 110 of the ultrasonic device 100. The bond lines 420 may mechanically isolate each membrane section 410 through attachment of the membrane 400 to the substrate 160 of the ultrasonic device 100. The membrane section 410 may be held above the top surface of the electromechanically active device 120 by the epoxy dot 330. The epoxy dot 330 may bond the tip of the electromechanically active device 120 slightly off the center of the membrane section 410. The membrane section 410 may cross over the channel 150, and may be bonded to the substrate 160 on either side of the channel 150.

FIG. 9B shows an example ultrasonic device according to an implementation of the disclosed subject matter. The membrane sections, such as membrane sections 410, 910, and 915, of the membrane 400 may be mechanically isolated from each other by the bond between the membrane 400 and the substrate 160 along the bond lines 420. For example, when the electromechanically active device 120 is activated and flexes upward, the membrane section 410 may be pushed upwards at the location of the epoxy dot 330. Because the epoxy dot 330 is slightly off center, the membrane section 410 may be pushed upwards at its center by the epoxy dot 330 and the flexed tip of the electromechanically active device 120. The bond lines 420 may mechanically isolate the membrane section 410 from neighboring membrane section 210, so that movement of the membrane section 410 due to movement of the electromechanically active device 120 does not cause any movement or disturbance of the membrane section 910. Similarly, the electromechanically active device 925 may be activated and flex upward, pushing up the membrane section 915. The neighboring membrane section 910 may be mechanically isolated from the membrane section 915 by the bond lines 420.

FIG. 10 shows a process suitable for membrane bonding according to an implementation of the disclosed subject matter. At 1000, an ultrasonic device may be cleaned. For example, the electromechanically active devices 120 of the ultrasonic device 100 may be cleaned using any suitable solvents. The solvents may be, for example, acetone, methanol, and isopropanol, or chromic acid, hydrochloric acid, or other materials that may promote adhesion.

At 1002, a surface of a membrane may be prepared for bonding. For example, a surface of the membrane 400 may be plasma cleaned, chemically etched, textured with sandpaper, an abrasive cleaning pad, or an abrasive slurry, and chemically activated with an adhesion promotor. The membrane 400 may made of aluminum shim stock, metal-patterned Kapton, other metal-patterned film, or any other suitable light, stiff material. After a surface of the membrane 400 is roughened, the membrane 400 may be cleaned, for example, with isopropanol.

At 1004, epoxy may be applied to the ultrasonic device. For example, the stencil 200 may be placed on the ultrasonic device 100, covering the ultrasonic transducers 110. An epoxy, which may be conductive or non-conductive, may be applied to the ultrasonic device 100 through openings or apertures in the stencil 200, such as the dashes 220 and the dots 230, using a metal straight edge or non-compliant rubber-backed squeegee. The epoxy may be mixed with glass microspheres, which may be between 25 micrometers and 100 micrometers in diameter. The stencil 200 may be patterned, for example, with dashed squares 210, and the epoxy may form the pattern of the stencil 200 on the ultrasonic device 100. The stencil 200 may be removed from the ultrasonic device 100 after application of the epoxy. The epoxy lines 320 may divide the ultrasonic device 100 into ultrasonic transducer cells 310. Each ultrasonic transducer cell 310 may include any number of ultrasonic transducers 110. For example, each ultrasonic transducer cell 310 may include a single ultrasonic transducer 110. The ultrasonic transducer cells 310 may have any suitable shapes, which may be determined by the pattern of the stencil 200.

At 1006, the roughened surface of the membrane may be placed on the epoxy on the ultrasonic device. For example, the roughened surface of the membrane 400 may be placed on the ultrasonic device 100 to be in contact with the epoxy. The membrane 400 may cover the ultrasonic transducers 110 of the ultrasonic device 100. In some implementations, the membrane 400 may cover only some of the ultrasonic transducers 110.

At 1008, the ultrasonic device with the membrane may be placed between flat plates. For example, the ultrasonic device 100 with the membrane 400 may be placed between flat plates 510 and 520. The bottom of the ultrasonic device 100 may be placed onto the flat plate 520, and the flat plate 510 may be placed on top of the membrane 400.

At 1010, light pressure may be applied to the membrane for the curing time of the epoxy. For example, the weight of the flat plate 510 may apply light pressure to the membrane 400, ensuring it remains in contact with the epoxy on the ultrasonic device 100, or pressure may be applied through the flat plate 510 using any suitable pressure providing device. The pressure may push the membrane 400 towards the ultrasonic device 100. The light pressure may be applied for the curing time of the epoxy. The curing time may be, for example, less than 48 hours, and the curing temperature may be less than 90 degrees Celsius. In some implementations, the light pressure may be removed before the end of the curing time. After the epoxy has cured, the membrane 400 may be bonded to the ultrasonic device 100 along bond lines 420 and at epoxy dots 330 on the tips of the electromechanically active devices 120. The bond lines 420 may create borders for ultrasonic transducer cells 310, which may each be covered by a membrane section 410 that may be mechanically isolated from other membrane sections 410 while still being part of the membrane 400.

The foregoing description, for purpose of explanation, has been described with reference to specific embodiments. However, the illustrative discussions above are not intended to be exhaustive or to limit embodiments of the disclosed subject matter to the precise forms disclosed. Many modifications and variations are possible in view of the above teachings. The embodiments were chosen and described in order to explain the principles of embodiments of the disclosed subject matter and their practical applications, to thereby enable others skilled in the art to utilize those embodiments as well as various embodiments with various modifications as may be suited to the particular use contemplated. 

The invention claimed is:
 1. A method comprising: applying a bonding agent to one or both of an ultrasonic device and membrane; placing the membrane on the ultrasonic device such that the membrane is in contact with the ultrasonic device through the bonding agent; placing the membrane and the ultrasonic device in between a first flat plate and a second flat plate, such that the second flat plate rests on top of the membrane; and applying light pressure to the membrane, wherein the light pressure is applied by one or more of the weight of the second flat plate and a pressure providing device applying pressure to either or both of the first flat plate and the second flat plate, wherein the bonding agent cures to form bond lines bonding the membrane to the ultrasonic device and wherein the bond lines divide the membrane into mechanically isolated membrane sections.
 2. The method of claim 1, wherein applying the bonding agent to the ultrasonic device comprises: placing a stencil on the ultrasonic device; and applying the bonding agent to the ultrasonic device through one or more openings in the stencil.
 3. The method of claim 2, wherein the stencil is placed on the ultrasonic device based on fiducials of the stencil and fiducials of a substrate of the ultrasonic device.
 4. The method of claim 2, wherein the openings of the stencil comprise dashes and dots, the dashes forming a grid of dashed squares with a dot at the center of each dashed square in the grid of dashed squares.
 5. The method of claim 2, wherein the bonding agent applied to the ultrasonic device creates borders of ultrasonic transducer cells, and wherein a dot of the bonding agent is applied to the tips of the free ends of electromechanically active devices of the ultrasonic device.
 6. The method of claim 2, wherein the bonding agent is applied using a metal straight-edge or a rubber squeegee.
 7. The method of claim 1, wherein the bonding agent is an epoxy.
 8. The method of claim 1, wherein the light pressure is applied for the entire curing time of the bonding agent.
 9. The method of claim 1, wherein each of the membrane sections is bonded by the cured bonding agent to the tip of the free end of an electromechanically active device covered by the membrane section.
 10. The method of claim 9, wherein the electromechanically active device is bonded to the membrane section off the center of the membrane section.
 11. The method of claim 9, wherein the electromechanically active device is a piezoelectric unimorph or a piezoelectric bimorph.
 12. The method of claim 1, further comprising keeping the membrane and ultrasonic device at a temperature below 90 degrees Celsius for the curing time of the bonding agent.
 13. The method of claim 1, further comprising, before placing the membrane on the ultrasonic device, preparing or texturing at least one surface of the membrane.
 14. The method of claim 1, wherein the membrane comprises a metal film.
 15. The method of claim 1, wherein the bonding agent is mixed with glass microspheres.
 16. The method of claim 1, wherein the ultrasonic device comprises one or more ultrasonic transducers on a substrate.
 17. The method of claim 1, wherein each ultrasonic transducer comprises an electromechanically active device attached to the substrate and partially projecting out over a cavity in the substrate. 